AARON ROSS and DAVID LEWIS GENERAL Mahamat Idriss Deby had been tipped to take over Chad's leadership from his father some day. But the elder Deby's death on the battlefield has meant that day came sooner than expected. Although the army leadership put on a show of unity when the 37-year-old was presented on national television on Tuesday as the country's new president and army commander-in-chief, holding them together will be his prime challenge, analysts say. Most of the senior officers are of the same battle-hardened generation as his father. Mahamat Idriss Deby - also known as Mahamat Kaka -…